Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 250455
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1055 PM MDT Mon Jul 24 2017

.UPDATE...
Issued at 846 PM MDT Mon Jul 24 2017

Thunderstorms have moved out of south central South Dakota. Still
a small risk of storms clipping far northwest South Dakota
overnight.

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 142 PM MDT Mon Jul 24 2017

Latest upper analysis shows an upper low crossing the Canadian
prairies with a trough extending southward into Montana. Weak
shortwave is crossing northeastern South Dakota trailing a weak
cold front into southwestern and south central South Dakota. South
of the boundary, temperatures are currently around 100F with
dewpoints in the lower 60s. Drier air is headed toward south
central South Dakota from the southwest. SBCAPE in the moist
sector has risen to around 2500J/KG and the cap is eroding as
noted by thunderstorms developing along the frontal boundary east
of Philip. During the rest of this afternoon, expect isolated to
scattered thunderstorms over south central SD with the activity
gradually shifting to the east during the evening as a low level
jet develops over central NEB and curves ahead of the sfc front
into northeastern SD. Isolated thunderstorms may also develop over
the Black Hills during the afternoon but any storms there are
expected to be short live, with the thunderstorm chances over the
Blkhls ending by early evening. Overnight the upper low in Canada
will continue to shift eastward a disturbance in the flow will
bring a slight chance of showers or thunderstorms to far
northeastern Wyoming and far northwestern South Dakota late
tonight.

On Tuesday, multiple surface boundaries consolidate across
southern portions of the forecast area. With a few weak
disturbances in the flow crossing the region. A better defined
shortwave will approach the forecast area during the afternoon,
leading to widespread precipitation, especially on Tuesday
evening. PW values will rise to 150-200% of normal as moisture
pools along the boundary creating 1-2KJ/kg MLCAPE and little MLCIN
by 00z. Could see some training storms and/or locally heavy rain.
0-6km bulk shear will be sufficient for isolated severe storms
Tuesday afternoon and evening. Temperatures will be near
guidance.

On Wednesday and Thursday, slightly cooler temperatures will occur
with TSRA possible, mainly over northeastern Wyoming and far
western South Dakota, as the upper ridge rebuilds over the western
CONUS.

Friday through Sunday, the upper ridge will build over the high
plains with warmer temperatures and small chances for
thunderstorms.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1054 PM MDT Mon Jul 24 2017

Isolated thunderstorms expected overnight across far northeast
Wyoming and far northwest South Dakota. Scattered thunderstorms
will develop across the area Tuesday afternoon and evening. Local
MVFR conditions possible with thunderstorms, otherwise VFR
conditions expected.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

Update...7
DISCUSSION...10
AVIATION...7



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